boost::time_period::span() returns invalid period if one of the periods is not-a-date-time

[willi.burkhardt@…]

In some cases, the time_period::span() function returns a less than optimal result. The expected behavior is that if one of the two periods is invalid/not-a-date-time the other is returned.

What I observed is that if one of the two source periods is not-a-date-time, the length() of the period returned is wrong/broken; invalidating the resulting time_period.

I might be wrong with my expectation above, but in this case it should be at least documented. Attached is a global function that I use to "fix" it in my code.

[Willi Burkhardt <willi.burkhardt@…>]

global function that I use as workaround for the problem